Add a hooks system, allowing users to specify a command to run, either before or after the approximation algorithm is run, for all schemes or one specific one.
Also rewrite :CSApproxSnapshot to be more maintainable and less of a hack, and fix several bugs that it contained.

Distribute an rgb.txt along with CSApprox, so that CSApprox can still be used on distributions where no rgb.txt is provided with the X server (like Ubuntu Intrepid Ibex). Thanks to Penn Su for finding this!